10 Essential Hippopotamus Facts

01
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How Much Do You Know About Hippos?

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With their broad mouths, their hairless bodies, and their semi-aquatic habits, hippopotamuses have always struck humans as vaguely comical creatures—but the fact is that a hippo in the wild can be almost as dangerous (and unpredictable) as a tiger or hyena. Here, you'll discover 10 essential facts about hippopotamuses, ranging from how these mammals got their names to how they were almost imported wholesale into the state of Louisiana.

02
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The Name "Hippopotamus" Means "River Horse"

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As is the case with so many other animals, the name "hippopotamus" derives from Greek—a combination of "hippo," meaning "horse," and "potamus," meaning "river." Of course, this mammal coexisted with human populations of Africa for thousands of years before the Greeks ever laid eyes on it, and is known by various extant tribes as the "mvuvu," "kiboko," "timondo," and dozens of other local variants. By the way, there's no right or wrong way to pluralize "hippopotamus:" some people prefer "hippopotamuses," others like "hippopotami," but you should always say "hippos" rather than "hippi." And what are groups of hippotamuses (or hippopotami) called? You can take your pick among herds, dales, pods, or (our favorite) bloats.

03
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Hippos Can Weigh Up to Two Tons

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Hippos aren't the world's largest land mammals—that honor belongs, by a hair, to the largest breeds of elephants and rhinoceroses—but they come pretty close. The biggest male hippos can approach three tons, and apparently never stop growing throughout their 50-year life span; the females are a few hundred pounds lighter, but every bit as menacing, especially when defending their young. Like most plus-sized mammals, hippotamuses are devoted vegetarians, mostly eating grass supplemented by various aquatic plants (though they have been known to consume meat when extremely hungry or stressed). Somewhat confusingly, hippos are classified as "pseudoruminants"—they're equipped with multiple-chambered stomachs, like cows, but they do not chew a cud (which, considering the huge size of their jaws, would make for a pretty comical sight).

04
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There Are Five Different Hippo Subspecies

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While there is only one hippopotamus species—Hippopotamus amphibius—there are five different subspecies, corresponding to the parts of Africa where these mammals live. H. amphibius amphibius, also known as the Nile hippopotamus or the great northern hippopotamus, lives in Mozambique and Tanzania; H. amphibius kiboko, the East African hippopotamus, lives in Kenya and Somalia; H. amphibius capensis, the South African hippo or the Cape hippo, extends from Zambia to South Africa; H. amphibius tchadensis, the West African or Chad hippo, lives in (you guessed it) western Africa and Chad; and the Angola hippopotamus, H. amphibius constrictus, is restricted to Angola, Congo and Namibia.

05
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Hippos Live Only in Africa

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As you might have inferred from the subspecies described above, hippopotamuses live exclusively in Africa (though they once had a more widespread distribution; see #7). The Internal Union for the Conservation of Nature estimates that there are between 125,000 and 150,000 hippos in central and southern Africa, a sharp drop from their census numbers in prehistoric times but still fairly healthy for your typical megafauna mammal. Their numbers have declined most precipitously in the Congo, in central Africa, where poachers and hungry soldiers have left only about 1,000 hippos standing out of a previous population of almost 30,000. (Unlike elephants, which are valued for their ivory, hippos don't have much to offer traders, with the exception of their enormous teeth—which are sometimes sold as ivory substitutes.)

06
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Hippos Have Almost No Hair

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One of the oddest things about hippopotamuses is their almost complete lack of body hair—a vaguely unnerving trait that puts them in the company of humans, whales, and a handful of other mammals. (Hippos have hair only around their mouths and on the tips of their tails.) To make up for this deficit, hippos do have extremely thick skin, consisting of about two inches of epidermis and only a thin layer of underlying fat (there's not much need to conserve heat in the wilds of equatorial Africa!) Most weirdly of all, evolution has endowed the hippo with its own natural sunscreen—a substance consisting of red and orange acids that absorbs ultraviolet light and inhibits the growth of bacteria. This has led to the widespread myth that hippos sweat blood; in fact, these mammals don't possess any sweat glands at all, which would be superfluous considering their semi-aquatic lifestyle.

07
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Hippos May Have Shared a Common Ancestor With Whales

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Unlike the case with rhinoceroses and elephants, the evolutionary tree of hippopotamuses is rooted in mystery. As far as paleontologists can tell, modern hippos shared a last common ancestor, or "concestor," with modern whales, and this presumed species lived in Eurasia about 60 million years ago, only five million years after the dinosaurs had gone extinct. Still, there are tens of millions of years bearing little or no fossil evidence, spanning most of the Cenozoic Era, until the first identifiable "hippopotamids" like Anthracotherium and Kenyapotamus appear on the scene. More reliably, it seems that the branch leading to the modern genus of hippopotamus split off from the branch leading to the pygmy hippopotamus (genus Choeropsis) less than ten million years ago. (The pygmy hippopotamus of western Africa weighs less than 500 pounds, but otherwise looks uncannily like a full-sized hippo.)

08
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A Hippo Can Open its Mouth Almost 180 Degrees

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Why do hippos have such enormous mouths? Their diets certainly have something to do with it—a two-ton mammal has to eat a lot of food to sustain its metabolism. But sexual selection also plays a major role: one of the likely reasons a male hippopotamus can open its mouth at a 180-degree angle is that this is a good way to impress females (and deter competing males) during mating season, the same reason that males are equipped with such enormous incisors, which otherwise would make no sense given their vegetarian menus. By the way, a hippo can chomp down on branches and leaves with a force of about 2,000 pounds per square inch, enough to cleave a luckless tourist in half (which occasionally happens during unsupervised safaris). By way of comparison, a healthy human male has a bite force of about 200 PSI, and a full-grown saltwater crocodile tilts the dials at 4,000 PSI.

09
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Hippos Spend Most of Their Day Submerged in Water

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If you ignore the difference in size, hippopotamuses may be the closest thing to amphibians in the mammal kingdom. When they're not grazing on grass—which takes them into the African lowlands for five or six hours at a stretch—hippos prefer to spend their time fully or partially submerged in freshwater lakes and rivers, and occasionally even in saltwater estuaries. Hippopotamuses have sex in the water—the natural buoyancy helps to protect the females from the suffocating weight of the males—fight in the water, and even give birth in the water. Amazingly, a hippo can even sleep underwater, as its autonomic nervous system prompts it to float to the surface every few minutes and take a gulp of air. The main problem with a semi-aquatic African habitat, of course, is that hippos have to share their homes with crocodiles, which occasionally pick off smaller newborns unable to defend themselves.

10
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It's Hard to Tell Male Hippos From Female Hippos

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Many animals, including humans, are sexually dimorphic—the males tend to be larger than the females (or vice-versa), and there are other ways, besides directly examining the genitals, to distinguish between the two sexes. A male hippo, though, looks pretty much exactly like a female hippo, with the exception of that 10 percent or so difference in weight—which makes it difficult for researchers in the field to investigate the social life of a lounging "bloat" of multiple individuals. (Of course, someone could volunteer to dive underwater and check out the hippos' undersides, but given the powerful bites described in #8 this sounds like a bad idea.) We do know that hippo "bulls" are sometimes surrounded by harems of a dozen or so females; otherwise, though, these mammals tend not to be social, preferring to bathe, swim, and feed all by themselves.

11
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Hippos Were Almost Imported Into the Louisiana Bayou

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One imagines that the wetlands, swamps and bayous of the southeastern U.S. would be a prime hippo vacation destination, assuming there was some way for these mammals to partake their bulk from Africa to the New World. Amusingly, back in 1910, a congressman from Louisiana proposed importing hippos into the bayous of Louisiana, where these beasts would supposedly rid the swamps of invasive water hyacinths and provide an alternative source of meat for nearby residents. (There don't seem to have been any provisions in the proposed bill for what Louisianans would do if the hippo population exploded out of control; one imagines the history of 20th-century America might have been very different.) Sadly, this imaginative piece of legislation failed to garner votes, so the only place you can see a hippo today in the U.S. is at your local zoo or wildlife park.

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Strauss, Bob. "10 Essential Hippopotamus Facts." ThoughtCo, Oct. 12, 2017, thoughtco.com/hippo-facts-4142336. Strauss, Bob. (2017, October 12). 10 Essential Hippopotamus Facts. Retrieved from https://www.thoughtco.com/hippo-facts-4142336 Strauss, Bob. "10 Essential Hippopotamus Facts." ThoughtCo. https://www.thoughtco.com/hippo-facts-4142336 (accessed January 22, 2018).